This invention relates to automatic cutting apparatus having steering controlled by an automatic optical tracking system.
Various remote control lawn mowers have been developed to mow grass or other vegetation without requiring the operator to steer the mower while riding on or walking behind it. Radio control is a common communication link. However, because the steering requires the full attention of the operator and because his ability to steer at a distance is limited by visibility, the marketing potential for this type of system is limited.
Other methods of self-tracking are within the state of the art but require expensive fixed installations of a track, either mechanically, electronically or magnetically coupled. Other systems require complex and costly triangulation systems to establish location. A lawn mower apparatus which cuts randomly within a boundary and drive means therefore are shown in U.S. Pat. No. 3,550,714 and 3,570,227, both to Bellinger. U.S. Pat. No. 3,566,988 to Wise shows a driverless lawn mower which mows a straight line path, reverses direction, steers an offset distance and continues. This cycle is repeated until the area is mowed. The Wise apparatus makes no provision for guidance correction means or tracking.
U.S. Pat. No. 3,425,197 to Kita shows an automatic lawn mower which tracks in an essentially spiral pattern to cut an area of grass utilizing mechanical sensors to detect cut and uncut areas. When a light detector senses cut grass, the right drive wheel stops, and when it senses uncut grass, the right wheel drives. When the left detector senses cut grass, the left wheel drives, and when it senses uncut grass, the left wheel stops. U.S. Pat. No. 3,235,023 to Gilmer shows a guidance system for land-working machinery which deposits a path of reflective spheres as it tracks in a generally spiral configuration. A light source of parallel rays is reflected from the path of spheres and the degree of light dispersion is detected. This system uses a light comparator for detecting differences measured by two photo detectors to operate a servo system.
An automatic lawn mower according to the present invention provides automatic and accurate guidance for a self-propelled lawn mower at a comparatively low cost without requiring a fixed installation tracking system or any control equipment in a remote location.
The presently disclosed apparatus includes a self-propelled lawn mower which provides a mobile platform for all tracking detection and guidance equipment to make it a self-contained automatic lawn mower. The apparatus might also be used for harvesting certain farm crops or for the removal of other vegetation. The presently disclosed embodiment provides engine power transfer through a differential to two rear wheels. In another embodiment, engine power transfer occurs through hydraulic coupling to the two rear wheels. All other wheels are castor wheels to permit steering by actuating a right or left brake which stops the respective right or left rear wheel. Drive power is applied only to the opposite rear wheel and a turn is thereby executed. Each brake is actuated by a solenoid which is controlled by guidance electronics on the mower platform. Provisions exist for manual steering to and from the mowing site, and double swivel action castor wheels are utilized to permit free movement during sharp turning maneuvers. The relative position of the two rear wheels with respect to the mower blades affects the maneuverability. These wheels are offset to the right to favor left turns enabling the mower to execute a right angle left turn without leaving uncut grass to the right of its path during the turn.
In another embodiment of the invention steering is accomplished by varying the speed ratio of the two independently driven rear wheels in proportion to the degree of steering error. Major steering error corrections and corner turning maneuverability are accomplished by powering one rear wheel forward and the other in reverse.
The automatic lawn mower embodiment presently disclosed is designed to track on the transition line between the cut and the uncut grass. The operator mows an outline boundary of the intended mowing area and mows a boundary around all obstacles which must be bypassed by the mower using a separate mowing device. The operator does not mow a path to and from the obstacle boundaries. A margin of uncut grass to the inside of an obstacle boundary is left for detection for tracking while the apparatus bypasses the obstacle. This pre-mowing establishes an outline pattern for automatic tracking. The automatic lawn mower apparatus is preprogrammed to provide right or left steering commands based upon the data received from a right and a left sensor while tracking the grass height transition within the mowing boundary.
The right sensor provides tracking data which causes the mower to cut grass in a normal mode. The right sensor has priority and when usable tracking data is no longer available from the right sensor, the left sensor is interrogated for recognition of obstacle bypass commands. If a transition line cannot be detected from either sensor, the mower executes a left turn until the right sensor regains control. This defines a normal left turn sequence.
If the left sensor recognizes an obstacle during a normal sequence, it retains guidance control and steers the left edge of the mower cutting path to the right of the tracking center line and tracks on the grass transition preset around the obstacle. The left sensor retains guidance control until the right sensor again recognizes a grass level transition line. The right sensor then regains control. This procedure defines the sequence where an obstacle is bypassed causing the mower to leave the straight line path of normal mowing, bypass the obstacle, and subsequently reunite with the straight line path.
The sensor detectors consist of a plurality of photoconductors passing a nearly constant current flow. The photoconductors are spaced at intervals on a line perpendicular to the grass transition line. The sensors have their own light source, and many comparisons of voltage across pairs of photoconductors are made. When the grass transition line falls between photoconductors of a pair being compared, a substantial voltage difference occurs. This occurs because the light intensity received by the photoconductors from the sensor light source is altered by the level of the grass. In another embodiment of the invention, the light intensity received by the photoconductors from the sensor light source is altered by the level of the grass through light switch actuators. The present mower apparatus utilizes a noise suppression circuit which also makes it possible to determine if the higher level grass is on the left or on the right of the grass transition line. The noise suppression circuit requires threshold level triggering before a photoconductor comparison difference is recognized.
Many comparator circuits supply data which is multiplexed into a single output to provide a scanning operation from left to right. The comparator spacings are set up to permit the grass transition line to fall between the detector pair of more than three comparators. Consequently, the multiplexer provides a short duration pulse when each of these comparators is sampled during a scan. The pulses are counted and a latch circuit is actuated when three pulses have been detected. Noise response is suppressed since three concurring comparator indications are required. When a third pulse is detected, an output logic 1 level signal is changed to a logic 0 signal. If the transition from a logic 1 to a logic 0 occurs midway in the scanning pattern and reoccurs each cycle, the on time of the waveform is equal to the off time. This condition represents a case where there is no guidance error, and the grass transition line is located centrally of the photoconductor array. An unbalance of the on and off times indicates a need for steering correction and indicates the direction of the correction necessary. This unbalance signal is used to apply a series RC circuit to a DC voltage source on the on interval and apply it to 0 volts on the off interval. The voltage across the capacitor then becomes a nominal DC voltage with a relatively small ripple superimposed.
In another embodiment of the present invention, the comparator spacings are set up to permit the grass transition line to fall between the detector pair of seven comparators. Consequently, the multiplexer provides a short duration pulse when each of these comparators is sampled during a scan. The pulses are counted and a latch circuit is actuated when four of six consecutive pulses have been detected. Noise response is suppressed since four concurring comparator indications are required. When a fourth pulse is detected, an output logic 1 level signal is changed to a logic 0 signal.
If the on and off intervals are balanced, the nominal DC voltage on the capacitor becomes half of the DC voltage source. A threshold circuit is then provided to command the mower steering to turn right if the nominal DC voltage across the capacitor exceeds a predetermined margin above normal and to turn left if it is less than normal by a predetermined margin. At the conclusion of mowing, the sensors can no longer detect a grass transition line, and the mower circles counterclockwise in the same manner it would to execute a left turn. After a preset time interval, the mower engine is turned off, and shortly thereafter, the electric power is removed from most circuitry.